1. Field of the Invention
The present invention relates to a transparent conductive film that has transparency in the visible light range and includes a film substrate and a transparent conductor layer provided on the substrate with an undercoat layer interposed therebetween, and also to a method for production thereof. The invention also relates to a touch panel including the transparent conductive film.
The transparent conductive film of the present invention may be used for transparent electrodes in touch panels and display systems such as liquid crystal displays and electroluminescence displays and also used for electromagnetic wave shielding or prevention of static charge of transparent products. In particular, the transparent conductive film of the present invention is preferably used for touch panels. The transparent conductive film of the invention is particularly suitable for use in resistive film type touch panels.
2. Description of the Related Art
Touch panels may be classified according to a position sensing method into an optical type, an ultrasonic type, a capacitive type, a resistive film type, and the like. Resistive film type touch panels are configured to include a pair of transparent conductive films arranged opposite to each other with spacers interposed therebetween, in which an electric current is allowed to flow through an upper transparent conductive film, while a voltage at a lower transparent conductive film is measured. When the upper transparent conductive film is brought into contact with the lower transparent conductive film by pressing with a finger, a pen or the like, the electric current flows through the contact portion so that the position of the contact portion is detected. Therefore, the transparent conductive films are required to have pen input durability.
In recent years, therefore, various types of plastic films such as polyethylene terephthalate films have been used as a substrate of such transparent conductive films, because of their advantages such as good impact resistance and light weight as well as flexibility and workability. Touch panels including such transparent conductive films are frequently used outdoors. Therefore, the transparent conductive films are required to have high-temperature, high-humidity reliability as well as pen input durability.
Incidentally, it is proposed that a transparent conductive film should include a transparent conductor layer with a controlled thickness of 12 to 2 nm, a controlled maximum surface roughness of 1 to 20 nm and a controlled average surface roughness of 0.1 to 10 nm (WO 2004/105055 Pamphlet). It is also proposed that the transparent conductive film should include two transparent conductor layers such that the surface roughness Ra may be controlled to be 0.5 to 2.0 nm and that the maximum height Ry may be controlled to be 8 to 20 nm (Japanese Patent Application Laid-Open (JP-A) No. 2005-268616). It is also proposed that the transparent conductive film should include a transparent conductor layer whose center line-average roughness Ra, ten-point-average roughness Rz and maximum height Ry are adjusted to 1 nm or less, 10 nm or less, and 10 nm or less, respectively, by polishing (Japanese Patent Application Laid-Open (JP-A) No. 2005-93318). WO 2004/105055 Pamphlet discloses that the transparent conductor layer may be obtained in a form of a very thin continuous film. Japanese Patent Application Laid-Open (JP-A) No. 2005-268616 discloses that the transparent conductor layer has low resistance and high surface smoothness. Japanese Patent Application Laid-Open (JP-A) No. 2005-93318 discloses that the surface of the transparent conductor layer has high smoothness. However, the transparent conductor layer described in each of the above documents does not provide both pen input durability and high-temperature, high-humidity reliability.